Abstract
Fifteen Ettawah-cross does were used to study maternal serum concentrations of total triiodothyronine ($T_3$), teraiodothyronine ($T_4$) and cortisol in different status of pregnancy (nonpregnant, aborted, single and twin-bearing does) during late pregnancy. Analysis of the data indicated that here was no significant changes in total $T_3$, $T_4$, and cortisol concentrations with the advance of pregnancy. Concentrations of $T_3$, $T_4$, and cortisol decreased by 38.9, 34.9, and 32.6%, and 12.0, 15.7 and 27.6%, and 41.6, 44.0, and 43.7% in the aborted, single and, twin-bearing, respectively, as compared to those nonpregnant does. These was no significant difference in concentrations of $T_3$ and cortisol between aborted, single and twin-bearing does, and in those of $T_4$ between aborted and single-bearing does. However, $T_4$ concentrations in twin-bearing were lower by 17.7 and 14.1% than those in aborted and single-bearing does, respectively. The decreased concentrations of thyroid hormones in pregnant does suggested that fetus could have increased iodine uptake from maternal circulation causing a decrease in the availability of this nutrient for synthesis of maternal thyroid hormones. The decreased concentrations of cortisol could have been associated with the increased metabolism of the hormone to regulate nutrients influx into the placenta of pregnant does.